Manitowoc Published 10-09-2020, Control # 259-06 2-21
MLC80A-1/MLC90A-1/MLC100A-1/MLC100-1 SERVICE/MAINTENANCE MANUAL HYDRAULIC SYSTEM
REPLACING PRESSURE TRANSDUCERS
Testing a Pressure Transducer
See Figure 2-16 for the following procedure.
Before replacing a pressure transducer, perform the
following test steps to verify the suspect pressure transducer
is faulty.
1. Perform a pressure transducer calibration as instructed
in the Main Display Operation Manual.
2. Stop the engine and turn the ignition switch to the RUN
position.
3. Attach an accurate hydraulic pressure gauge to the
gauge coupler at the suspect pressure transducer.
4. If pressure appears on the gauge, bleed the
corresponding system so the gauge reads zero pressure
(see step 9
).
5. Repeat the pressure transducer calibration and check
the pressure on the calibration display with the engine
running at idle. The display reading and the gauge
reading should be the same.
6. Before replacing a pressure sender, check the electric
signal voltage at the sender. It should be 4 mA at zero
pressure.
Replacing a Pressure Transducer
To replace a pressure transducer, perform the following
procedure.
1. Lower all loads to the ground.
2. Move all control handles to OFF and park all crane
functions.
3. Stop the engine.
4. Place a suitable container under the faulty pressure
transducer to catch hydraulic oil leakage.
5. Disconnect the electrical connector from the pressure
transducer.
6. Slowly loosen the pressure transducer only enough to
relieve the pressure.
7. Remove the pressure transducer and discard it and the
oil leakage according to local environmental regulations.
8. Install the new pressure transducer and connect the
electrical connector.
9. Bleed the pressure transducer circuit as follows.
a. Connect a bleed line with a shut-off valve to the
pressure transducer gauge coupler and place the
end of the hose into a suitable container.
b. Open the shut-off valve.
c. With all control handles off, start and run the engine
at low idle.
d. When clear oil flows from the bleed line (no air
bubbles in the oil), close the shut-off valve.
e. Stop the engine.
f. Remove the bleed line from the gauge coupler at
the pressure transducer.
g. Repeat the above steps for each new pressure
transducer.
10. Perform the pressure transducer calibration.
SHOP PROCEDURES
Initial Hydraulic Oil Fill
See Figure 2-12, page 15 for the following procedure.
The following procedure is used at the factory to fill the
hydraulic system on a new crane. It is necessary to use this
procedure in the field only if the entire hydraulic system has
been drained.
1. Open the hydraulic tank shut-off valve (10).
2. Open the Schrader valve (3) or the vent valve (4)
located on top of the tank (1). Failure to do this will result
in over pressurizing the tank. Fill hydraulic tank to the
appropriate level depending on cylinder position using
the manual fill port.
Do not fill the hydraulic tank through the desiccant
breather (5) or the top of the Filters. The hydraulic
system could be contaminated from unfiltered oil.
WARNING
High Pressure Oil Hazard!
Do not attempt to remove a pressure transducer until the
following steps are performed. High pressure oil will
exhaust from the pressure transducer ports.
Hot Oil Hazard!
Take precautions to prevent being burned by hot oil.
WARNING
Burn Hazard!
The oil in the hydraulic tank may be under pressure and
extremely hot. Hot oil can escape when servicing
components.
Before opening the tank for any reason, relieve any
pressure from the tank using the Schrader valve or the
vent valve (see Figure 2-12, page 15
).
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